First, create two new fields in your table "Created", and "LastModified" as "datetime" fields, being sure to allow nulls. Then run this code as a query to create triggers that will update the appropriate field when a record is modified, or a record is inserted. This proves very useful when you're dealing with a huge database.

In the code below replace [TableName] with your actual table name, and replace [UniqueID] with a unique ID field name in your table.